Carrier telegraphy



April v4, 1950 R. B. sHANcK 2,503,000 CARRIER TELEGRAPHY Filed DGO. 25,1947 ATTORNEY Patented Apr. 4, 1950 UNITED STATES PATENT OFFICETelephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 23, 1947,Serial No. 793,555

The invention relates to two-way carrier wave signaling systems andparticularly to two-way carrier telegraph systems.

The invention is specifically applicable to a system operating toprovide two-way carrier telegraph communication between a number ofstations located at diierent points over a common two-wire circuit, suchas a telephone line. Diiculty has been experienced in the operation ofisuch multipoint systems due to echo effects. Such difficulties havebeen obviated in prior art carrier telegraph systems of this type by theprovision of means at each station for desensitizing or disabling thesignal receiving equipment while outgoing signals are being transmittedfrom the station and for a short time interval thereafter, so as toprevent false operation of this equipment by the portion of the outgoingsignals or echoes thereof diverted into the receiving circuit at thecommon point of connection of the signal transmitting and receivingcircuits to the common line. This method, of course, has disadvantagesin that it results inr lockout or loss of any incoming signals receivedat the sending station over the common line from other stations duringthe period of desensitization or disablement of the receiving equipmentat the first station, and prevents another station from breaking-induring this time interval.

An object of the invention is to improve such lmultipoint carriertelegraph systems.

Other objects are to reduce the effects of sender echoes; to preventtransmission lockouts; and to facilitate break-in by any station in sucha multipoint carrier telegraph system when another station istransmitting signals.

In the improved multipoint carrier telegraph system in accordance withthe invention, the carrier transmitters of a considerable number oftwo-way carrier telegraph stations connected over a common two-way line,operate on respecquencies incoming over the line from all of the otherstations. Thus, when any station is sending, false operation of thereceiving equipment of that station either directly in response to thetransmitted signals or bytalker echoes is prevented, and any receivingstation can break in at 3 Claims. (Cl. 8l-2) any time to transmit itscarrier signals to the receiving equipment of the first station.

The various objects and features of the invention are brought out moreclearly in the following complete description to be read in conjunctionwith the accompanying drawing, the single figure of which showsschematically a multipoint carrier telegraph system embodying theinvention.

In the system oi the invention as shown in the drawing, a plurality ofsubscriber carrier telegraph stations l, 2, 3, 4, 5, 6 are connected tothe two-wire line L at diierent points. Station l`, as indicated,includes the sending oscillator S01 designed to generate carrieroscillation of the frequency F1, which may be of any suitable type,having its output connected directly across the line L, and thereceiving wave detector RDi having its input connected across the line Lthrough a band elimination nlter BEF1 designed to suppress applied Wavesof frequency corresponding to the transmitting frequency F1 assigned tostation l and to provide substantially free transmission of the carrierwaves of the frequencies transmitted by all the other stations, 2, 3, 4,5, t to the receiving detector RD1. The station may include any suitablesource of outgoing telegraph signals for keying the sending oscillatorS01 and any suitable telegraph signal receiving equipment controlledfrom the output of the detector RD1, for example, teletypewritertransmitting and receiving equipment of the type disclosed in the UnitedStates Patent 1,904,164, issued on April 18, 1933, to S. Morton et al.The subscriber teletypewriter equipment TTY1, as illustrateddiagrammatically, may include a neutral receiving relay or device 1,which may be the selector magnet of a printing telegraph recorder suchas is disclosed in the aforementioned Mortcn et al. patent; atransmitting device including transmitting contacts 8; and a break key 9all of which are connected inA a direct current or local telegraphcircuit, shown as a conventional balanced loop circuit, in series withthe battery l0 and the resistor l I across the two series windings ofthe polar relay PR1. One output terminal of the receiving detector'RD1'is connected to a point between the two series windingsof polar relayPE1 and the other output terminal to ground. In the idle condition ofthe station, that is, when no outgoing telegraph signals are beingtransmitted, the armature of relay PRl is held on its marking contacts Mto connect biasing battery l2 to the sending oscillator S01 inoscillator 501,]802

such manner as to bias it to the unoperated condition.

Each of the other subscriber stations 2, 3, 4, 5, 6 comprises equipmentidentical with that of station I as described above, as indicated by theuse of similar identification characters for the component elementsexcept for the addition of a subscript identifying it with theparticular station (see stations 2 and 6 illustratedl in detail), exceptthat the respective sending oscillators S02, S03, S04, S05, S06 in thesestations are designed to generate carrieroscillations of the differentrespective frequencies F2, F3, F4, F5, Fs and the bandelimination filterBEFz, BEF3, BEFq, BEFs, BEFs inllhe input of the receiving circuit ofeach station is'respectively designed to suppressfapplied wavesoffrequency corresponding to the transmittingfrequency, F2, Fs, F4, F5,or Fs assigned respectively to these stationsand to providesubstantially free transmissionv of the carrierwaves-of the frequenciestransmitted byall the other stations. to theassociatedreceiving'detector.

The transmitting contacts 8 in the teletypewriter equipment TTY1, TTYz'at each vof g thestations I, '2 may be controlled by` a keyboardmechanism such as disclosed in the aforementioned Morton et al. patentto control the associated polar relay PR1, PRz of the station inaccordance with permutation code signals representing a telegraphmessage. .With ,the

, break key 9 closed and the transmitting contacts 8 `oftheteletypewriter equipment ata station in the rest or idle conditionindicated, which isa marking condition, the windings of the asso-.,ciatedf-polar relay PE1, PRz .-are operatively energized from theassociated battery II)y to hold .,therarmature of that relay onitsmarking M" v Contact. 4Whenthe break key 9 or the associatedcircuitis open the .armature ofthe associated polar relay PE1, PRz isreturned to the spac- ,ing S contact. The, operation ofthe armature ofthe polar relay PR1, PRz to ,the lmarking contact connects the biasingbattery I2 to the .associated sending oscillator S01, S02 in suchmanneras to bias it to the unoperated condition soV that .no carrier`oscillations are transmitted to theline L, and 4eachoperation ofthe`armature of this relay to the spacing contact will remove the biasingbattery to key 4the associated so that` it transmits a train of carrieroscillations of theassigned frequency F2 of .the,station, representing aspacing telegraphrsignal out over theline L.

i It will be assumed that the subscriber at-sta- -tion IY-is operating`the. keyboard of his teletypewriter-equipment TTY1 so as toalternatelyshift the armature of the polar relay PE1' from the marking to thespacing contact in accordance with the permutation code signals of atelegraph message, causing the sending oscillator S01 to bekeyedperiodically so as to send out over the line L trains of carrieroscillations of the frequency F1 representing'the telegraph message. Anyportion of these outgoing carrier signals, or echoes thereof,l enteringthe receiving circuit of station I at"itspoint of connection to thelinelL will be 'prevented from Ireaclfiingfthe receiving .detector RD1and causing false operation', thereof by the :band'ilter BEF1ini theinput :of that detector,

which-is designed to suppress waves of the frequency F1.

AThe carrier signals-of thefrequen'cy Frincom- 4 elimination lter BEFz,BEFa BEFe in the receiving circuit of each of the other stations 2 6,the pass ranges of which include the frequency F1, and will be detectedby the receiving detector in the output thereof, and the detectedsignals will be supplied through the upper Winding of the associatedpolar relay to the se- "lectorffrelay' in the teletypewriterf equipmentlat each station controlling the latter relay in accordance with theincoming telegraph mes- Sage.

Now, let it be assumed that while station I continues to send outcarrier signals of the frequen- 1 cy-'Fr-overthe line L, the subscriberat another station, sas/,station 6, desires to break in. He

will operate his break key 9 and the teletypewriterv equipment TTYs,which, in the manner described aboveY in connection with the similarequipment at station I, will cause the keying of the sending oscillatorS06 so that it sends out .-trainsiof carrier oscillations of thefrequency Fn and `will be detected by the receiving detector RD1 in itsoutput. Equal portions of the direct current signaloutput of thereceiving detector RD1 will pass inopposite directionsr through theupperand lower windings of the polar relay PE1 so that they will-have noresultant effect on the armature of .that relay. Theportion of thedetected signals passing through the upper winding of tl'ie'polary relayPR1 will `be supplied to vthe selector relay T of the teletypewriterequipment lT'IY1, and will control that relay in accordance with-thebreak or spacing signals from-station 6.

Similarly; the receiving selector magnet I in the teletypewriterequipment at each of theother stations 3 to S'will be controlled inaccordance `with the signals from station 6.

`In' the manner described, to-and^fro carrier telegraph communicationbetween all` thecarriertelegraph stations over the single-line L can beobtained without appreciable transmission *lo'ckeouts and without dangerof false operation carrier'telegraph system may be operated with as manyas seventeen or eighteen stations on broad-band facilities and withabout fourteen on the narrower band type C carrier telephone facilities.A narrower spacing, such as 120 cycles,

could be used for ordinary speeds and allow the use Yof almost 50 percent more stations on any one circuit. Except when transmitting witheither the highest or lowest carrier frequency,

VVeach receiving station would vreceive signals through a fairly widefrequency bandso that the wave shape would be nearly rectangular. ,Onlyone receiving station would be operated by an appreciably rounded wavein case the highest v or lowest carrier frequency. were used. There-- ffore,...theeffects of normal attenuation changes would be reducedmaterially in such a system `as compared vto thosefin the system`employing rounded wave shapes.

Various modifications Vof the circuits illustrated t.. and, describedwhichare within the spirit and rscope ofL .theinvention will occurto'persons nLskiued ,in the. art.

What is claimed is:

1. A carrier telegraph communication system comprising a transmissionline and a plurality of subscriber stations connected to said line atdifferent points, each of said stations including means for sending outtrains of carrier oscillations of a frequency which is different foreach station, representing telegraph signals over said line to the otherstations and receiving means responsive to the telegraphsignal-representing carrier oscillations of other frequencies incomingover said line from all of the other stations, but substantiallyunresponsive to applied carrier oscillations of the frequencytransmitted from the local station, or echoes thereof.

2. A carrier telegraph communication system comprising a transmissionline and a plurality of subscriber stations connected to said line atdifferent points, each of said stations including a source of carrieroscillations of a frequency which is different for each station,connected to said line, means to key said carrier source in accordancewith telegraph signals so that it transmits trains of carrieroscillations representing said signals out over said line to the otherstations, telegraph signal receiving means responsive to the carriersignals of other frequencies incoming over said line and means toprevent false operation of said telegraph signal receiving means inresponse to the carrier signals transmitted from the station, or echoesthereof, comprising filtering means connected between said line and saidtelegraph signal receiving means, designed to provide substantialattenuation in applied waves of the frequency of said transmittedcarrier signals and substantially negligible attenuation to appliedwaves of frequencies corresponding to those of the carrier signalstransmitted from all the other stations.

3. A multipoint carrier telegraph communication system comprising atwo-Wire transmission line and a plurality of subscriber stationsconnected to said line at different points, each station comprising asending oscillator adapted to generate carrier oscillations of afrequency Which is different for each subscriber station, feeding intosaid line, transmitting means for keying said sending oscillator inaccordance With signals to be transmitted so that it transmits trains ofcarrier oscillations of the frequency assigned to the station,representing said signals out over said line to the other stations, aWave detector connected to said line for detecting the carrier signalsof other frequencies incoming over said line from all of said otherstations, telegraph receiving means responsive to the detected signaloutput of said detector and a band elimination filter connected betweensaid line and said Wave detector, designed to prevent Waves of thefrequency of the carrier signals transmitted from said station fromreaching said detector while allowing substantially free transmissionthereto of the carrier signals of the different frequencies incomingover said line from all of the other stations.

ROY B. SHANCK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,816,904 Horton Aug. 4, 19312,047,900 Bruckel July 14, 1936 2,393,021 Cheek Jan. 14, 1946

